Jorge, welcome. "Everywhere" apparently doesn't include here, because probably a majority of the opinion has been to use QSs for rear surrounds as well. This may be because of the overall excellence of the QSs, which you've already discovered. Another factor is the seating arrangement in the room. You haven't described how far you are from the back wall where the surrounds would be. The closer that you are, the more likely that the wider dispersion of the QSs would have the advantage, since the direct radiators wouldn't have room to spread enough for good surround effects at such close range.
If you could temporarily borrow some small direct speakers(if you don't have any around)to try in back it might make your decision easier. You could also temporarily move your QS8s back there for a comparison.
